Yup, that's the https://en.wikipedia.org/wiki/Default_mode_network
It's the daydreaming/mind-wandering state that occurs when you're not focused on an external task. With all the stimuli of the modern world, I feel like we're being starved of crucial DMN time if we don't engineer conditions like the ones you describe.
Quite the interesting but unapproachable topic. Doesn't help that neurology logic on brain-level is dynamic and general rules are hard to extract.